A novel androgen receptor splice variant is up-regulated during prostate cancer progression and promotes androgen depletion-resistant growth

Discovery of Novel Bifunctional Agents as Potent Androgen Receptor Antagonists and Degraders for the Treatment of Enzalutamide-Resistant Prostate Cancer

Bifunctional agents that simultaneously antagonize and degrade various AR proteins more effectively block the AR signaling pathway, offering a promising strategy for the treatment of mCRPC patients. Herein, we report the discovery and development of a series of small-molecule AR degraders with 3,8-diazabicyclo[3.2.1]octan scaffold. The optimal compound 20i exhibited potent AR antagonistic and degrading activities, effectively overcoming multiple resistance mechanisms and showing significant antiproliferative effects against enzalutamide-resistant PCa cell lines. Moreover, compound 20i exhibited favorable oral pharmacokinetics and a good safety profile. In the 22Rv1 xenograft models, 20i exhibited potent antitumor activity without obvious toxicity. Taken together, these results demonstrated that 20i might be a potential candidate for the treatment of enzalutamide-resistant PCa.

Combined Transcriptomic and Epitranscriptomic Profiling Identifies THBS1 as A Regulator of Enzalutamide Resistance in Prostate Cancer

Cancer drug resistance arises not only from selection of resistant clones, but also through rapid activation of adaptive transcriptional programs. One mechanism of transcriptional regulation involves N6-methyladenosine (m6A) RNA modification, which dynamically regulates mRNA processing and alternative splicing, ultimately impacting cell fate and differentiation. In prostate cancer (PC), resistance to systemic therapies such as the androgen receptor pathway inhibitor (ARPI) enzalutamide is associated with a host of well-documented androgen receptor (AR) alterations, including amplification, mutation, and alternative splicing. Given these functions, we hypothesized that m6A modifications play a role in the transition to enzalutamide resistance in PC. To test this, we used methyl-RNA-immunoprecipitation followed by sequencing (MeRIP-seq) in parallel with RNA-seq to identify gene transcripts that were both differentially methylated and differentially expressed between enzalutamide-sensitive and enzalutamide-resistant PC cells. We filtered and prioritized these genes using clinical and functional database tools, including Gene Ontology (GO) enrichment analysis and Gene Set Enrichment Analysis (GSEA), The Cancer Genome Atlas (TCGA), and the Oncology Research Information Network (ORIEN) avatar. Using this approach, we identified 487 transcripts that were both differentially methylated and differentially expressed and validated six of the top 12 candidates via targeted qPCR and MeRIP-PCR. One of these, THBS1, was found to have increased m6A level associated with decreased transcript levels in enzalutamide-resistant cells, a finding recapitulated in publicly available preclinical and clinical data. Moreover, in enzalutamide-sensitive cells, depletion of THBS1 by siRNA-knockdown induced resistance to enzalutamide. While THBS1 has previously been implicated in aggressive PC phenotypes, we now show that THBS1 downregulation directly contributes to a rapid transition to enzalutamide resistance, suggesting a novel role for this gene in PC hormonal therapy resistance. These results constitute the first comprehensive epitranscriptomic profiling of ARPI resistance and identify THBS1 as a potential driver of acute resistance in prostate cancer.

Androgen receptor-regulated lncRNA PRCAT71 promotes AR signaling through the interaction with KHSRP in prostate cancer

Mounting evidence indicates that long noncoding RNAs (lncRNAs) play vital roles in tumorigenesis and progression of cancers. However, the functions and regulatory mechanisms of lncRNAs in prostate cancer (PCa) are still largely unknown. In this study, we found an lncRNA, PCa-associated transcript 71 (PRCAT71), highly expressed in metastatic and primary PCa compared to benign prostate tissues. Silencing PRCAT71 inhibited cancerous properties of PCa cells and androgen receptor (AR) signaling. Mechanistically, PRCAT71 acts as a scaffold to recruit K homology (KH)-type splicing regulatory protein (KHSRP) to AR messenger RNA (mRNA) and stabilize AR mRNA, leading to activated AR signaling. KHSRP plays a critical role in PCa progression. PRCAT71 is transcriptionally regulated by AR-driven enhancers, forming a positive regulatory loop between AR and PRCAT71 in PCa. Our study demonstrates a coordinated regulation of AR mRNA by lncRNA PRCAT71 and RNA binding protein KHSRP and provides insight that the PRCAT71-KHSRP-AR axis is a promising therapeutic target for treating PCa.

Triple-negative breast cancer molecular subtypes and potential detection targets for biological therapy indications

Triple-negative breast cancer (TNBC) is a highly aggressive subtype of breast cancer associated with poor prognosis. While chemotherapy remains the conventional treatment approach, its efficacy is limited and often accompanied by significant toxicity. Advances in precision-targeted therapies have expanded treatment options for TNBC, including immunotherapy, poly (ADP-ribose) polymerase inhibitors, androgen receptor inhibitors, cell cycle-dependent kinase inhibitors, and signaling pathway inhibitors. However, the heterogeneous nature of TNBC contributes to variations in treatment outcomes, underscoring the importance of identifying intrinsic molecular subtypes for personalized therapy. Additionally, due to patient-specific variability, the therapeutic response to targeted treatments is inconsistent. This highlights the need to strategize patients based on potential therapeutic targets for targeted drugs to optimize treatment strategies. This review summarizes the classification strategies and immunohistochemical (IHC) biomarkers for TNBC subtypes, along with potential targets for identifying indications for targeted drug therapy. These insights aim to support the development of personalized treatment approaches for TNBC patients.

Discovery of novel spirocyclic derivates as potent androgen receptor antagonists

We report herein the development of a series of novel AR antagonists characterized by a spirocyclic scaffold, employing scaffold hopping and structure-based drug design strategies. Most of the spirocyclic derivatives exhibited enhanced AR antagonistic activity and superior antiproliferative activity against LNCaP cells compared to enzalutamide. Among them, compound 21 demonstrated moderate antiproliferative activity against enzalutamide resistant prostate cancer cell lines and exhibited favorable in vitro metabolic stability. These findings offer valuable insights for the rational design of AR antagonists for the treatment of advanced prostate cancer.

Targeting the CLK2/SRSF9 splicing axis in prostate cancer leads to decreased ARV7 expression

In advanced prostate cancer (PC), in particular after acquisition of resistance to androgen receptor (AR) signaling inhibitors (ARSI), upregulation of AR splice variants compromises endocrine therapy efficiency. Androgen receptor splice variant-7 (ARV7) is clinically the most relevant and has a distinct 3' untranslated region (3'UTR) compared to the AR full-length variant, suggesting a unique post-transcriptional regulation. Here, we set out to evaluate the applicability of the ARV7 3'UTR as a therapy target. A common single nucleotide polymorphism, rs5918762, was found to affect the splicing rate and thus the expression of ARV7 in cellular models and patient specimens. Serine/arginine-rich splicing factor 9 (SRSF9) was found to bind to and increase the inclusion of the cryptic exon 3 of ARV7 during the splicing process in the alternative C allele of rs5918762. The dual specificity protein kinase CLK2 interferes with the activity of SRSF9 by regulating its expression. Inhibition of the Cdc2-like kinase (CLK) family by the small molecules cirtuvivint or lorecivivint results in the decreased expression of ARV7. Both inhibitors show potent anti-proliferative effects in enzalutamide-treated or -naive PC models. Thus, targeting aberrant alternative splicing at the 3'UTR of ARV7 by disturbing the CLK2/SRSF9 axis might be a valuable therapeutic approach in late stage, ARSI-resistant PC.

Insulin-Like Growth Factor 2 mRNA-Binding Protein 2 (IGF2BP2) Promotes Castration-Resistant Prostate Cancer Progression by Regulating AR-V7 mRNA Stability

BACKGROUND

The emergence of constitutively active androgen receptor (AR) splice variant AR-V7 poses a formidable challenge in treating prostate cancer, as it lacks the ligand binding region targeted by androgen-deprivation therapies such as enzalutamide and abiraterone. AR-V7 is critical for castration-resistant prostate cancer (CRPC) development and progression; however, the molecular mechanisms regulating its expression and biological function remain poorly understood. Here, we investigate the role of IGF2BP2 in regulating AR-V7 expression and CRPC progression.

METHODS

To determine the clinical relevance of IGF2BP2 in CRPC, we analyzed the mRNA expression data for prostate cancer patients available in the Genomic Data Commons (GDC) Data Portal and cBioPortal. Next to investigate the role of IGF2BP2 in regulating AR-V7 expression and enzalutamide resistance, we performed shRNA-mediated IGF2BP2 knockdown and overexpression experiments followed by qRT-PCR, immunoblot, colony-formation, and MTT assays. Finally, we performed RIP-qPCR, actinomycin-D, and IGF2BP2 domain-deletion analysis to study the mechanism by which IGF2BP2 regulates AR-V7 stability, expression, and enzalutamide resistance in CRPC cells.

RESULTS

Our analysis revealed that IGF2BP2 is upregulated in CRPC patients and its expression positively correlates with increasing Gleason score in patients with CRPC. We demonstrate that IGF2BP2 silencing leads to downregulation of AR-V7 and its downstream target genes without affecting AR levels. Additionally, IGF2BP2 knockdown also enhances the sensitivity of CRPC cells to enzalutamide while overexpression increases AR-V7 expression and confers increased resistance to enzalutamide. Mechanistically, our experiments demonstrate that IGF2BP2 binds to the intronic splicing enhancer (ISE) region of AR-V7, thereby enhancing its mRNA stability. Furthermore, our domain-deletion analysis pinpoints the role of KH3 and KH4 domains of IGF2BP2 in regulating AR-V7 stability and enzalutamide resistance.

CONCLUSIONS

Taken together, our findings suggest that IGF2BP2 plays a critical role in regulating AR-V7 expression and stability, offering a novel target for developing therapeutic interventions for CRPC.

Increased nuclear factor I-mediated chromatin access drives transition to androgen receptor splice variant dependence in prostate cancer

Androgen receptor (AR) splice variants, of which ARv7 is the most common, are increased in castration-resistant prostate cancer, but the extent to which they drive AR activity is unclear. We generated a subline of VCaP cells (VCaP16) that is resistant to the AR inhibitor enzalutamide (ENZ). AR activity in VCaP16 is driven by ARv7, independently of full-length AR (ARfl), and its cistrome and transcriptome mirror those of ARfl in VCaP cells. ARv7 expression increases rapidly in response to ENZ, but there is a delay in gaining chromatin binding and transcriptional activity, which is associated with increased chromatin accessibility. AR and nuclear factor I (NFI) motifs are most enriched at more accessible sites, and NFIB/X knockdown greatly diminishes ARv7 function. These findings indicate that ARv7 can drive the AR program but that its activity is dependent on adaptations that increase chromatin accessibility to enhance its intrinsically weak chromatin binding.

A novel peptide encoded by circSRCAP confers resistance to enzalutamide by inhibiting the ubiquitin-dependent degradation of AR-V7 in castration-resistant prostate cancer

BACKGROUND

The sustained activation of androgen receptor splice variant-7 (AR-V7) is a key factor in the resistance of castration-resistant prostate cancer (CRPC) to second-generation anti-androgens such as enzalutamide (ENZ). The AR/AR-V7 protein is regulated by the E3 ubiquitin ligase STUB1 and a complex involving HSP70, but the precise mechanism remains unclear.

METHODS

High-throughput RNA sequencing was used to identify differentially expressed circular RNAs (circRNAs) in ENZ-resistant and control CRPC cells. The coding potential of circSRCAP was confirmed by polysome profiling and LC-MS. The function of circSRCAP was validated in vitro and in vivo using gain- and loss-of-function assays. Mechanistic insights were obtained through immunoprecipitation analyses.

RESULTS

A novel ENZ-resistant circRNA, circSRCAP, was identified and shown to be upregulated in ENZ-resistant C4-2B (ENZR-C4-2B) cells, correlating with increased AR-V7 protein levels. circSRCAP is generated via splicing by eIF4A3, forming a loop structure and is exported from the nucleus by the RNA helicase DDX39A. Mechanistically, circSRCAP encodes a 75-amino acid peptide (circSRCAP-75aa) that inhibits the ubiquitination of AR/AR-V7's co-chaperone protein HSP70 by disrupting the interaction with the E3 ligase STUB1. This process results in the upregulation of AR-V7 expression and promotes ENZ resistance in CRPC cells. Xenograft tumor models further confirmed the role of circSRCAP in CRPC progression and its potential as a therapeutic target for ENZ-resistant CRPC.

CONCLUSIONS

circSRCAP provides an epigenetic mechanism influencing AR-V7 stability and offers a promising therapeutic target for treating ENZ-resistant CRPC.

Looking beyond the ER, PR, and HER2: what's new in the ARsenal for combating breast cancer?

Breast cancer (BrCa) is a complex and heterogeneous disease with diverse molecular subtypes, leading to varied clinical outcomes and posing significant treatment challenges. The increasing global burden of BrCa, particularly in low- and middle-income countries, underscores the urgent need for more effective therapeutic strategies. The androgen receptor (AR), expressed in a substantial proportion of breast cancer cases, has emerged as a potential biomarker and therapeutic target. In breast cancer, AR exhibits diverse functions across subtypes, often interacting with other hormone receptors, thereby influencing tumor progression and treatment responses. This intricate interplay is further complicated by the presence of constitutively expressed AR splice variants (AR-Vs) that drive resistance to AR-targeting therapies through structural rearrangements in the domains and activation of aberrant signaling pathways. Although AR-targeting drugs, initially developed for prostate cancer (PCa), have shown promise in AR-positive breast cancer, significant gaps remain in understanding AR's precise functions and therapeutic potential. The systemic management of breast cancer is guided primarily by theranostic biomarkers; ER, PR, HER2, and Ki67 which also dictate the breast cancer classification. The ubiquitous expression of AR in BrCa and the emergence of AR-Vs can assist the management of disease complementing the standard of care. This article provides a comprehensive overview of AR and its splice variants in the context of breast cancer, highlighting their prognostic and predictive value across different subtypes looking beyond the conventional ER, PR, and HER2 status. This review also raises the possibility of using AR splice variants in predicting tumor aggressiveness. From the settings of developing nations, this may provide useful insight by integrating recent advances in AR-targeted therapies and exploring their translational potential, emphasizing the critical need for further research to optimize AR-based therapeutic strategies for breast cancer management.

Higher isoform of hnRNPA1 confer Temozolomide resistance in U87MG & LN229 glioma cells

BACKGROUND

Gliblastoma is a malignant brain tumor; despite available treatment modalities, the tumor reoccurrence rate persist in the currently prescribed Temozolomide chemotherapy. Study aimed to study the inquisitive role of RNA binding splice factor protein hnRNPA1 in promoting glioma resistance against Temozolomide drug and therapeutic insights.

METHODS

In this study two non-expressing O6-methylguanine-DNA methyltransferase (MGMT) glioma cell lines U87MG & LN229. U87MG cells were grown in Temozolomide from 50μM upto 400μM & LN229 cells grown upto 200μM, till then both these cells acquired Temozolomide resistance. Both of these cells were grown & maintained continously in its highest dose of Temozolomide (TMZ). Splice factor protein SF2/ASF1 was functionally correlated with abundance of hnRNPA1 protein in Temozolomide (TMZ) resistant cells using its specific siRNA transfection approach, in detrmining SF2/ASF1 mediated hnRNPA1 splicing and Temozolomide resistant reversal.

RESULTS

U87MG TMZ resistance, results an increase in the expression of pre mRNA-splicing factor SF2/ASF1, Heterogeneous Ribonucleoprotein A1 (hnRNPA1) and O6-methylguanine-DNA methyltransferase (MGMT) protein. MGMT expression was not observed in LN229 TMZ resistant cells. Further, mRNA sequencing of hnRNPA1 confirmed the exclusive abundance of its higher isoform in TMZ- resistant cells along with increase in SF2/ASF1 expression. Knocking down of SF2/ASF1 using its specific siRNA reverted the higher isoform of hnRNPA1 isoform Var2 to its lower isoform hnRNPA1 Var1 in U87 TMZ resistant cells, reveals hnRNPA1 alternative higher isoform abundance is SF2/ASF1 splice factor dependent. Additionally, selective knock down of hnRNPA1 higher isoform Var2 in TMZ resistant U87MG & LN229 promotes apoptosis, was further specfically enhanced on Wortmannin (PI3Kinase inhibitor) treatment.

CONCLUSION

Targeting higher isoform Var2 of hnRNPA1 specifically induces chemosensitization in MGMT expressed Temozolomide resistant U87MG as well as in MGMT non-expressed LN229 TMZ resistant cells.

Targeting proliferating cell nuclear antigen enhances ionizing radiation-induced cytotoxicity in prostate cancer cells

BACKGROUND

Proliferating cell nuclear antigen (PCNA) is essential for DNA replication and repair, cell growth, and survival. PCNA also enhances androgen receptor (AR) signaling in prostate cancer (PC) cells. We identified a PCNA interaction protein (PIP) box at the N-terminal domain of AR and developed a small peptide PCNA inhibitor R9-AR-PIP containing AR PIP-box. We also identified a series of small molecule PCNA inhibitors (PCNA-Is) that bind directly to PCNA and interrupt PCNA functions. The present study investigated the effects of the PCNA inhibitors on the sensitivity of PC cells to X-ray radiation.

METHODS

The effects of targeting PCNA on radio sensitivity of PC cells were investigated in four lines of castration-resistant PC (CRPC) cells with different AR expression statuses. The cells were treated with the PCNA inhibitors and X-ray radiation alone or in combination. The effects of the treatment on expression of AR target genes, DNA damage response, DNA damage, homologous recombination repair (HRR), and cytotoxicity were evaluated.

RESULTS

We found that the androgen response element (ARE) occupancy of the DNA damage response gene PARP1 by AR is significantly attenuated by PCNA-I1S or R9-AR-PIP combined with X-ray radiation, while X-ray radiation alone does not enhance the ARE occupancy. PCNA-I1S or R9-AR-PIP alone significantly inhibits occupancy of the AR-occupied regions (AROR) in PRKDC and XRCC2 genes. R9-AR-PIP and PCNA-I1S inhibit expression of AR-Vs target gene cyclin A2 and show the additive effects with radiation in AR-positive CRPC cells. Targeting PCNA by PCNA-I1S and R9-AR-PIP downregulates expression of DNA damage response genes EXO1, Rad54L, Rad51, and/or PARP1 and shows the additive effects with radiation as compared with their respective controls in AR-positive CRPC LNCaP-AI, 22Rv1, and R1-D567 cells, but not in AR-negative PC-3 cells. R9-AR-PIP and PCNA-I1S elevate the levels of phospho-DNA-PKcs(S2056) and γH2AX, indicating DNA damage in response to radiation in AR-positive cells. The HRR is significantly attenuated by PCNA inhibitors PCNA-I1S, R9-AR-PIP, and T2AA in all four CRPC cells examined, and inhibited by Enzalutamide (Enz) only in 22RV1 cells. The cytotoxicity induced by X-ray radiation in androgen-dependent LNCaP cells is enhanced by Enz and a lower concentration of R9-AR-PIP in the colony formation assay. R9-AR-PIP at higher concentration reduces the colony formation and has an additive effect with X-ray radiation in all AR expressing cells, regardless of AR-FL and AR-Vs, but does not significantly alter the colony formation in AR-negative PC-3 cells. PCNA-I1S attenuates colony formation and has an additive effect with ionizing radiation in all four CRPC cells, regardless of AR expression status.

CONCLUSION

These data provide a strong rationale for the therapy studies using PCNA-I1S or R9-AR-PIP in combination with X-ray radiation against CRPC tumors in preclinical models.

Gastrin-releasing peptide receptor (GRPR) as a novel biomarker and therapeutic target in prostate cancer

Aim: This comprehensive review aims to explore the potential applications of Gastrin-releasing peptide receptor (GRPR) in the diagnosis and treatment of prostate cancer. Additionally, the study investigates the role of GRPR in prognostic assessment for individuals afflicted with prostate cancer.Methods: The review encompasses a thorough examination of existing literature and research studies related to the upregulation of GRPR in various tumor types, with a specific focus on prostate. The review also evaluates the utility of GRPR as a molecular target in prostate cancer research, comparing its significance to the well-established Prostate-specific membrane antigen (PSMA). The integration of radionuclide-targeted therapy with GRPR antagonists is explored as an innovative therapeutic approach for individuals with prostate cancer.Results: Research findings suggest that GRPR serves as a promising molecular target for visualizing low-grade prostate cancer. Furthermore, it is demonstrated to complement the detection of lesions that may be negative for PSMA. The integration of radionuclide-targeted therapy with GRPR antagonists presents a novel therapeutic paradigm, offering potential benefits for individuals undergoing treatment for prostate cancer.Conclusions: In conclusion, this review highlights the emerging role of GRPR in prostate cancer diagnosis and treatment. Moreover, the integration of radionuclide-targeted therapy with GRPR antagonists introduces an innovative therapeutic approach that holds promise for improving outcomes in individuals dealing with prostate cancer. The potential prognostic value of GRPR in assessing the disease's progression adds another dimension to its clinical significance in the realm of urology.

L1CAM mediates neuroendocrine phenotype acquisition in prostate cancer cells

BACKGROUND

A specific type of prostate cancer (PC) that exhibits neuroendocrine (NE) differentiation is known as NEPC. NEPC has little to no response to androgen deprivation therapy and is associated with the development of metastatic castration-resistant PC (CRPC), which has an extremely poor prognosis. Our understanding of genetic drivers and activated pathways in NEPC is limited, which hinders precision medicine approaches. L1 cell adhesion molecule (L1CAM) is known to play an oncogenic role in metastatic cancers, including CRPC. However, the impact of L1CAM on NEPC progression remains elusive.

METHODS

L1CAM expression level was investigated using public gene expression databases of PC cohorts and patient-derived xenograft models. L1CAM knockdown was performed in different PC cells to study in vitro cell functions. A subline of CRPC cell line CWR22Rv1 was established after long-term exposure to abiraterone to induce NE differentiation. The androgen receptor-negative cell line PC3 was cultured under the tumor sphere-forming condition to enrich cancer stemness features. Several oxidative stress inducers were tested on PC cells to observe L1CAM-mediated gene expression and cell death.

RESULTS

L1CAM expression was remarkably high in NEPC compared to CRPC or adenocarcinoma tumors. L1CAM was also correlated with NE marker expressions and associated with the adenocarcinoma-to-NEPC progression in gene expression databases and CRPC cells with NE differentiation. L1CAM also promoted cancer stemness and NE phenotypes in PC3 cells under cancer stemness enrichment. L1CAM was also identified as a reactive oxygen species-induced gene, by which L1CAM counteracted CRPC cell death triggered by ionizing radiation.

CONCLUSIONS

Our results unveiled a new role of L1CAM in the acquisition of the NE phenotype in PC, contributing to the NE differentiation-related therapeutic resistance of CRPC.

Prognostic role of Androgen Receptor splice variant 7 (AR-V7) in the pathogenesis of breast cancer

BACKGROUND

The Androgen Receptor (AR) has emerged as an endocrine therapy target in Breast Cancer, exhibiting up to 80% expression in clinical cases. AR-V7, a constitutively activated splice variant of AR with a truncated ligand-binding domain (LBD), demonstrates ligand-independent transcriptional activity and resistance to nonsteroidal antiandrogens like Bicalutamide or Enzalutamide, targeting the LBD. In metastatic prostate cancer, elevated AR-V7 levels lead to therapeutic resistance and increased metastasis.

METHODS

In this study, we evaluated the expression of AR and AR-V7 in cell lines and a cohort of 89 patients undergoing surgical intervention for treatment-naïve breast cancer. Further clinicopathological correlations and survival analysis were performed to evaluate the relationship between the AR and AR-V7 expression and clinical outcomes.

RESULTS

AR-V7/AR-FL ratio was elevated in the TNBC cell line and downregulation of AR-FL upon AR antagonists' treatment led to a compensatory increase in AR-V7. Clinical samples showed significantly elevated expression of AR and AR-V7 in tumors compared to control cases. Further clinicopathological correlation revealed aggressive clinical traits, higher pathological grades, and poor survival with AR-V7 expression.

CONCLUSIONS

Our study unravels AR-V7 as a marker for poor clinical outcomes, predicting breast cancer aggressiveness, and encourages consideration of AR-V7 as a probable target for therapeutic intervention.

Vaccination Against Androgen Receptor Splice Variants to Immunologically Target Prostate Cancer

Background/Objectives: Androgen receptor (AR) expression and signaling are critical for the progression of prostate cancer and have been the therapeutic focus of prostate cancer for over 50 years. While a variety of agents have been developed to target this axis, many of these fail due to the emergent expression of AR RNA splice variants, such as AR-V7, that can signal independently of ligand binding. Other therapies, such as vaccination against prostate-specific antigens, have achieved FDA approvals but have fallen short of being incorporated as standard-of-care therapies for advanced prostate cancer. This may be due to the elevated level of immunosuppression observed in prostate cancer, which remains largely refractory to immune checkpoint blockade. Methods: We developed a vaccine targeting AR-V7, a common isoform associated with treatment resistance, and demonstrated its ability to elicit AR-V7-specific immunity and enable anti-tumor responses against AR-V7+ cancers in subcutaneous tumor models. Results: Our studies also revealed that AR-V7 expression conferred an immune suppressive phenotype that was significant in a non-AR-dependent prostate cancer model. Notably, in this model, we found that vaccination in combination with enzalutamide, an AR antagonist, suppressed these aggressive immune suppressive cancers and resulted in enhanced survival in comparison to control vaccinated and enzalutamide-treated mice. While anti-PD-1 immune checkpoint inhibition (ICI) alone slowed tumor growth, the majority of vaccinated mice that received anti-PD-1 therapy showed complete tumor elimination. Conclusions: Collectively, these results validate the importance of AR signaling in prostate cancer immune suppression and suggest the potential of AR-V7-specific vaccines as therapeutic strategies against prostate cancer, offering significant protective and therapeutic anti-tumor responses, even in the presence of androgen signaling inhibitors.

LX1 Dual Targets AR Variants and AKR1C3 in Advanced Prostate Cancer Therapy

The development of resistance to current standard-of-care treatments, such as androgen receptor (AR) targeting therapies, remains a major challenge in the management of advanced prostate cancer. There is an urgent need for new therapeutic strategies targeting key resistant drivers, such as AR variants like AR-V7, and steroidogenic enzymes, such as aldo-keto reductase 1C3 (AKR1C3), to overcome drug resistance and improve outcomes for patients with advanced prostate cancer. Here, we have designed, synthesized, and characterized a novel class of LX compounds targeting both the AR/AR variants and AKR1C3 pathways. Molecular docking and in vitro studies demonstrated that LX compounds bind to the AKR1C3 active sites and inhibit AKR1C3 enzymatic activity. LX compounds were also shown to reduce AR/AR-V7 expression and to inhibit their target gene signaling. LX1 inhibited the conversion of androstenedione into testosterone in tumor-based ex vivo enzyme assays. In addition, LX1 inhibited the growth of cells resistant to antiandrogens including enzalutamide (Enza), abiraterone, apalutamide, and darolutamide in vitro. A synergistic effect was observed when LX1 was combined with antiandrogens and taxanes, indicating the potential for this combination in treating resistant prostate cancer. Treatment with LX1 significantly decreased tumor volume, serum PSA levels, as well as reduced intratumoral testosterone levels, without affecting mouse body weight. Furthermore, LX1 was found to overcome resistance to Enza treatment, and its combination with Enza further suppressed tumor growth in both the CWR22Rv1 xenograft and LuCaP35CR patient-derived xenograft models. Collectively, the dual effect of LX1 in reducing AR signaling and intratumoral testosterone, along with its synergy with standard therapies in resistant models, underscores its potential as a valuable treatment option for advanced prostate cancer. Significance: LX1 simultaneously targets androgen receptor variants and the steroidogenic enzyme AKR1C3, offering a promising approach to combat drug resistance and enhancing therapeutic efficacy in conjunction with standard treatments for advanced prostate cancer.

Current uses and resistance mechanisms of enzalutamide in prostate cancer treatment

INTRODUCTION

Prostate cancer continues to be a major cause of morbidity and mortality for men worldwide. Enzalutamide, a second-generation non-steroidal antiandrogen that blocks androgen receptor (AR) transcriptional activity, is a treatment for biochemically recurrent, metastatic, castration-sensitive, and castration-resistant tumors. Unfortunately, most patients ultimately develop resistance to enzalutamide, making long-term treatment with this agent challenging.

AREAS COVERED

We performed a literature search of PubMed without date restrictions to investigate the literature surrounding enzalutamide and discuss the current uses of enzalutamide, proposed mechanisms driving resistance, and summarize current efforts to mitigate this resistance.

EXPERT OPINION

Enzalutamide is an effective prostate cancer therapy that is currently used in biochemically recurrent and metastatic disease and for both castration-sensitive and castration-resistant tumors. Unfortunately, resistance to enzalutamide occurs in each of these scenarios. In the clinical setting, enzalutamide-resistant tumors are either AR-driven or AR-indifferent. AR-dependent resistance mechanisms include genomic or epigenomic events that result in enhanced AR signaling. Tumors that do not require AR signaling instead may depend on alternative oncogenic pathways. There are numerous strategies to mitigate enzalutamide resistance, including concurrent use of PARP inhibitors or immune therapies. Additional work is required to uncover novel approaches to treat patients in the enzalutamide-resistant setting.

Stromal androgen signaling governs essential niches in supporting prostate development and tumorigenesis

Androgens and androgen receptor (AR) mediated signaling pathways are essential for prostate development, morphogenesis, growth, and regeneration. Early tissue recombination experiments showed that AR-deficient urogenital sinus mesenchyme combined with intact urogenital sinus epithelium failed to develop into a prostate, demonstrating a stem cell niche for mesenchymal AR in prostatic development. Androgen signaling remains critical for prostate maturation and growth during postnatal stages. Importantly, most primary prostate cancer (PCa) cells express the AR, and aberrant activation of AR directly promotes PCa development, growth, and progression. Therefore, androgen deprivation therapy (ADT) targeting the AR in PCa cells is the main treatment for advanced PCa. However, it eventually fails, leading to the development of castration-resistant PCa, an incurable disease. Given these clinical challenges, the oncogenic AR action needs to be reevaluated for developing new and effective therapies. Recently, an essential niche role of stromal AR was identified in regulating prostate development and tumorigenesis. Here, we summarize the latest discoveries of stromal AR niches and their interactions with prostatic epithelia. In combination with emerging clinical and experimental evidence, we specifically discuss several important and long-term unanswered questions regarding tumor niche roles of stromal AR and highlight future therapeutic strategies by co-targeting epithelial and stromal AR for treating advanced PCa.

Protein isoform-centric therapeutics: expanding targets and increasing specificity

Most protein-coding genes produce multiple protein isoforms; however, these isoforms are commonly neglected in drug discovery. The expression of protein isoforms can be specific to a disease, tissue and/or developmental stage, and this specific expression can be harnessed to achieve greater drug specificity than pan-targeting of all gene products and to enable improved treatments for diseases caused by aberrant protein isoform production. In recent years, several protein isoform-centric therapeutics have been developed. Here, we collate these studies and clinical trials to highlight three distinct but overlapping modes of action for protein isoform-centric drugs: isoform switching, isoform introduction or depletion, and modulation of isoform activity. In addition, we discuss how protein isoforms can be used clinically as targets for cell type-specific drug delivery and immunotherapy, diagnostic biomarkers and sources of cancer neoantigens. Collectively, we emphasize the value of a focus on isoforms as a route to discovering drugs with greater specificity and fewer adverse effects. This approach could enable the targeting of proteins for which pan-inhibition of all isoforms is toxic and poorly tolerated.

Castration-resistant prostate cancer monitoring by cell-free circulating biomarkers

Background

Prostate cancer is the second leading cause of male cancer-related deaths in Western countries, which is predominantly attributed to the metastatic castration-resistant stage of the disease (CRPC). There is an urgent need for better prognostic and predictive biomarkers, particularly for androgen receptor targeted agents and taxanes.

Methods

We have searched the PubMed database for original articles and meta-analyses providing information on blood-based markers for castration-resistant prostate cancer monitoring, risk group stratification and prediction of therapy response.

Results

The molecular markers are discussed along with the standard clinical parameters, such as prostate specific antigen, lactate dehydrogenase or C-reactive protein. Androgen receptor (AR) alterations are commonly associated with progression to CRPC. These include amplification of AR and its enhancer, point mutations and splice variants. Among DNA methylations, a novel 5-hydroxymethylcytosine activation marker of TOP2A and EZH2 has been identified for the aggressive disease. miR-375 is currently the most promising candidate among non-coding RNAs and sphingolipid analysis has recently emerged as a novel approach.

Conclusions

The promising biomarkers have the potential to improve the care of metastatic prostate cancer patients, however, they need further validation for routine implementation.

Reactivation of nucleases with peroxidation damages induced by a menadione: ascorbate combination devastates human prostate carcinomas: ultrastructural aspects

INTRODUCTION

Xenografts of androgen-independent human DU145 prostate metastatic carcinomas implanted in nu/nu male mice have revealed a significant survival after a prooxidant anticancer treatment consisting of a combination of menadione bisulfite and sodium ascorbate (VK3:VC).

METHODS

Implanted samples of diaphragm carcinomas from longest survived mice from either oral, intraperitoneal (IP), or both oral and IP treatment groups were assessed with light, scanning, and transmission electron microscopy to analyze morphologic damages.

RESULTS

Compared with previous fine structure data of in vitro untreated carcinomas, the changes induced by oral, IP, and oral with IP VK3:VC treatment dismantled those xenografts with autoschizis, and necrotic atrophy was accomplished by cell's oxidative stress whose injuries were consequent to reactivated deoxyribonucleases and ribonucleases. Tumor destructions resulted from irreversible damages of nucleus components, endoplasmic reticulum, and mitochondria there. Other alterations included those of the cytoskeleton that resulted in characteristic self-excisions named " autoschizis." All these injuries lead resilient cancer cells to necrotic cell death.

CONCLUSION

The fine structure damages caused by VK3:VC prooxidant combination in the human DU145 prostate xenografts confirmed those shown in vitro and of other cell lines with histochemistry and biomolecular investigations. These devastations incurred without damage to normal tissues; thus, our data brought support for the above combination to assist in the treatment of prostate cancers and other cancers.

Synergistic Strategies for Castration-Resistant Prostate Cancer: Targeting AR-V7, Exploring Natural Compounds, and Optimizing FDA-Approved Therapies

Castration-resistant prostate cancer (CRPC) remains a significant therapeutic challenge due to its resistance to standard androgen deprivation therapy (ADT). The emergence of androgen receptor splice variant 7 (AR-V7) has been implicated in CRPC progression, contributing to treatment resistance. Current treatments, including first-generation chemotherapy, androgen receptor blockers, radiation therapy, immune therapy, and PARP inhibitors, often come with substantial side effects and limited efficacy. Natural compounds, particularly those derived from herbal medicine, have garnered increasing interest as adjunctive therapeutic agents against CRPC. This review explores the role of AR-V7 in CRPC and highlights the promising benefits of natural compounds as complementary treatments to conventional drugs in reducing CRPC and overcoming therapeutic resistance. We delve into the mechanisms of action underlying the anti-CRPC effects of natural compounds, showcasing their potential to enhance therapeutic outcomes while mitigating the side effects associated with conventional therapies. The exploration of natural compounds offers promising avenues for developing novel treatment strategies that enhance therapeutic outcomes and reduce the adverse effects of conventional CRPC therapies. These compounds provide a safer, more effective approach to managing CRPC, representing a significant advancement in improving patient care.

Evaluation of androgen receptor and androgen receptor splice-variant 7 in bladder cancer; a novel approach into an ancient topic

PURPOSE

The contribution of androgen receptors (AR) on bladder cancer has been demonstrated in pre-clinical studies, however in clinical studies, only the canonical AR (AR-FL) protein was measured by immunohistochemistry and conflicting results were obtained. To get better insight into the alterations of AR signalling, we used western blotting (WB) method and simultaneously measured both mRNA and protein levels of AR-FL and AR-V7.

METHODS

23 naive non-muscle invasive bladder cancer patients and 12 healthy individuals were included. AR-FL protein, AR-FL mRNA, AR-V7 protein and AR-V7 mRNA levels were quantitatively measured by WB and qRT-PCR.

RESULTS

While AR-FL protein and AR-V7 mRNA were significantly higher in bladder cancer, AR-FL mRNA and AR-V7 protein were lower. AR-V7 mRNA level was higher in patients with tumour size over 3 cm and AR-FL protein was higher in single tumours (p < 0,005). The small sampling size and the inclusion of only male participants were the main limitations.

CONCLUSIONS

The increase of AR-FL protein in bladder cancer supports the contribution of the AR pathway in bladder cancer. The presence of high AR-FL protein despite low mRNA levels may be due to a disruption in post-transcriptional regulatory mechanisms. AR-V7 was demonstrated for the first time in bladder tissue and found significantly different in bladder cancer tissues. Our study reached new and valuable findings and will shed light on the studies that aim to clarify the role of the AR pathway in bladder cancer.

Discovery of novel biphenyl derivatives as androgen receptor degraders for the treatment of enzalutamide-resistant prostate cancer

Second-generation AR antagonists, such as enzalutamide, are the primary therapeutic agents for advanced prostate cancer. However, the development of both primary and secondary drug resistance leads to treatment failures and patient mortality. Bifunctional agents that simultaneously antagonize and degrade AR block the AR signaling pathway more completely and exhibit excellent antiproliferative activity against wild-type and drug-resistant prostate cancer cells. Here, we reported the discovery and optimization of a series of biphenyl derivatives as androgen receptor antagonists and degraders. These biphenyl derivatives exhibited potent antiproliferative activity against LNCaP and 22Rv1 cells. Our discoveries enrich the diversity of small molecule AR degraders and offer insights for the development of novel AR degraders for the treatment of enzalutamide-resistant prostate cancer.

Androgen receptor: Structure, signaling, function and potential drug discovery biomarker in different breast cancer subtypes

The Androgen Receptor (AR) is emerging as an important factor in the pathogenesis of breast cancer (BC), which is the most common malignancy worldwide. >70 % of AR expression in primary and metastatic breast tumors has been observed which suggests that AR may be a new marker and a potential therapeutic target among AR-positive BC patients. Biological insight into AR-positive breast cancer reveals that AR may cross-talk with several vital signaling pathways, including key molecules and receptors. Downstream signaling of AR might also affect many clinically important pathways that are emerging as clinical targets in BC. AR exhibits different behaviors depending on the breast cancer molecular subtype. Preliminary clinical research using AR-targeted drugs, which have already been FDA-approved for prostate cancer (PC), has given promising results for AR-positive breast cancer patients. However, since AR positivity's prognostic and predictive value remains uncertain, it is difficult to identify and stratify patients who would benefit from AR-targeted therapies alone. Thus, the need of the hour is to target the androgen receptor as a monotherapy or in combination with other conventional therapies which has proven to be an effective clinical strategy for the treatment of prostate cancer patients, and these therapeutic strategies are increasingly being investigated in breast cancer. Therefore, in this manuscript, we review the role of AR in various cellular processes that promote tumorigenesis and aggressiveness, in different subtypes of breast cancer, as well as discuss ongoing efforts to target AR for the more effective treatment and prevention of breast cancer.

Increased chromatin accessibility mediated by nuclear factor I drives transition to androgen receptor splice variant dependence in castration-resistant prostate cancer

Androgen receptor (AR) splice variants, of which ARv7 is the most common, are increased in prostate cancer (PC) that develops resistance to androgen signaling inhibitor drugs, but the extent to which these variants drive AR activity, and whether they have novel functions or dependencies, remain to be determined. We generated a subline of VCaP PC cells (VCaP16) that is resistant to the AR inhibitor enzalutamide (ENZ) and found that AR activity was independent of the full-length AR (ARfl), despite its continued high-level expression, and was instead driven by ARv7. The ARv7 cistrome and transcriptome in VCaP16 cells mirrored that of the ARfl in VCaP cells, although ARv7 chromatin binding was weaker, and strong ARv7 binding sites correlated with higher affinity ARfl binding sites across multiple models and clinical samples. Notably, although ARv7 expression in VCaP cells increased rapidly in response to ENZ, there was a long lag before it gained chromatin binding and transcriptional activity. This lag was associated with an increase in chromatin accessibility, with the AR and nuclear factor I (NFI) motifs being most enriched at these more accessible sites. Moreover, the transcriptional effects of combined NFIB and NFIX knockdown versus ARv7 knockdown were highly correlated. These findings indicate that ARv7 can drive the AR program, but that its activity is dependent on adaptations that increase chromatin accessibility to enhance its intrinsically weak chromatin binding.

Deciphering the genetic and epigenetic architecture of prostate cancer

Prostate cancer, one of the most frequently diagnosed cancers in men, leads to significant mortality worldwide. Its study is important due to the complexity and diversity in its progression, highlighting the urgent need for improved therapeutic strategies. This chapter probes into the genetic and epigenetic factors influencing prostate cancer progression, underscoring the importance of understanding the disease's molecular fundamentals for the development of targeted therapies. It specifically reviews the role of key genetic mutations in genes such as Androgen Receptor, TP53, SPOP, FOXA1 and PTEN which are crucial for the disease onset and a progression. Furthermore, it examines the impact of epigenetic modifications, including DNA methylation and histone modification, which contribute to the cancer's progression by affecting gene expression and cellular behavior. Further, in this chapter we delve into the underlying signaling mechanism, the advancements in targeting genetic and epigenetic alterations in prostate cancer. These findings have revealed promising targets for therapeutic advancements, aiming to understand and identify promising avenues for future therapies. This chapter improves our current understanding of prostate cancer genetic and epigenetic landscape, emphasizing the necessity of advancing our knowledge to refine and expand treatment options for prostate cancer patients.

Caffeic acid phenethyl ester suppresses the expression of androgen receptor variant 7 via inhibition of CDK1 and AKT

Androgen receptor (AR) splice variant 7 (AR-V7) is capable to enter nucleus and activate downstream signaling without ligand. AR-V7 assists the tumor growth, cancer metastasis, cancer stemness, and the evolvement of therapy-resistant prostate cancer (PCa). We discovered that caffeic acid phenethyl ester (CAPE) can repress the expression and downstream signaling of AR-V7 in PCa cells. CAPE blocked the gene transcription, nuclear localization, and protein abundance of AR-V7. CAPE inhibited the expression of U2AF65, SF2 and hnRNPF, which were splicing factors for AR-V7 intron. Additionally, CAPE decreased protein stability of AR-V7 and enhanced the proteosome-degradation of AR-V7. We observed that CDK1 and AKT regulated the expression and stability of AR-V7 via phosphorylation of Ser81 and Ser213, respectively. CAPE decreased the expression of CDK1 and AKT. Overexpression of CDK1 restored the abundance of AR-V7 in CAPE-treated PCa cells. Overexpression of AR-V7, AKT or CDK1 rescued the proliferation of PCa cells under CAPE treatment. Intraperitoneal injection of 10 mg/kg CAPE retarded the growth of 22Rv1 xenografts in nude mice and suppressed the protein levels of AR-V7, CDK1 and AKT in 22Rv1 xenografts. Our study provided the rationale of applying CAPE for inhibition of AR-V7 in prostate tumors.

Novel selective agents for the degradation of AR/AR-V7 to treat advanced prostate cancer

The androgen receptor AR antagonists, such as enzalutamide and apalutamide, are efficient therapeutics for the treatment of prostate cancer (PCa). Even though they are effective at first, resistance to both drugs occurs frequently. Resistance is mainly driven by aberrations of the AR signaling pathway including AR gene amplification and the expression of AR splice variants (e.g. AR-V7). This highlights the urgent need for alternative therapeutic strategies. Here, a total of 24 compounds were synthesized and biologically evaluated to disclose compound 20i, exhibiting potent AR antagonistic activities (IC50 = 172.85 ± 21.33 nM), promising AR/AR-V7 protein degradation potency, and dual targeting site of probably AR (ligand-binding domain, LBD and N-terminal domain, NTD). It potently inhibits cell growth with IC50 values of 4.87 ± 0.52 and 2.07 ± 0.34 μM in the LNCaP and 22RV1 cell lines, respectively, and exhibited effective tumor growth inhibition (TGI = 50.9 %) in the 22RV1 xenograft study. These data suggest that 20i has the potential for development as an AR/AR-V7 inhibitor with degradation ability to treat advanced prostate cancer.

SC912 inhibits AR-V7 activity in castration-resistant prostate cancer by targeting the androgen receptor N-terminal domain

Androgen deprivation therapies (ADT) are the mainstay treatments for castration-resistant prostate cancer (CRPC). ADT suppresses the androgen receptor (AR) signaling by blocking androgen biosynthesis or inhibiting AR with antiandrogens that target AR's ligand-binding domain (LBD). However, the ADT's effect is short-lived, as the AR signaling inevitably arises again, which is frequently coupled with AR-V7 overexpression. AR-V7 is a truncated form of AR that lacks the LBD, thus being constitutively active in the absence of androgens and irresponsive to AR-LBD-targeting inhibitors. Though compelling evidence has tied AR-V7 to drug resistance in CRPC, pharmacological inhibition of AR-V7 is still an unmet need. Here, we discovered a small molecule, SC912, which binds to full-length AR as well as AR-V7 through AR N-terminal domain (AR-NTD). This pan-AR targeting relies on the amino acids 507-531 in the AR-NTD. SC912 also disrupted AR-V7 transcriptional activity, impaired AR-V7 nuclear localization and DNA binding. In the AR-V7 positive CRPC cells, SC912 suppressed proliferation, induced cell-cycle arrest, and apoptosis. In the AR-V7 expressing CRPC xenografts, SC912 attenuated tumor growth and antagonized intratumoral AR signaling. Together, these results suggested the therapeutic potential of SC912 for CRPC.

Treatments Targeting the Androgen Receptor and Its Splice Variants in Breast Cancer

Breast cancer is a major cause of death worldwide. The complexity of endocrine regulation in breast cancer may allow the cancer cells to escape from a particular treatment and result in resistant and aggressive disease. These breast cancers usually have fewer treatment options. Targeted therapies for cancer patients may offer fewer adverse side effects because of specificity compared to conventional chemotherapy. Signaling pathways of nuclear receptors, such as the estrogen receptor (ER), have been intensively studied and used as therapeutic targets. Recently, the role of the androgen receptor (AR) in breast cancer is gaining greater attention as a therapeutic target and as a prognostic biomarker. The expression of constitutively active truncated AR splice variants in breast cancer is a possible mechanism contributing to treatment resistance. Therefore, targeting both the full-length AR and AR variants, either through the activation or suppression of AR function, depending on the status of the ER, progesterone receptor, or human epidermal growth factor receptor 2, may provide additional treatment options. Studies targeting AR in combination with other treatment strategies are ongoing in clinical trials. The determination of the status of nuclear receptors to classify and identify patient subgroups will facilitate optimized and targeted combination therapies.

Experimental treatment efficacy of dmrFABP5 on prostate cancer singly or in combination with drugs in use

Enzalutamide is a drug used to treat prostate cancer (PC) and docetaxel is a drug for chemotherapeutic treatment of diverse cancer types, including PC. The effectiveness of these drugs in treating castration-resistant prostate cancer (CRPC) is poor and therefore CRPC is still largely incurable. However, the bio-inhibitor of fatty acid-binding protein 5 (FABP5), dmrFABP5, which is a mutant form of FABP5 incapable of binding to fatty acids, has been shown recently to be able to suppress the tumorigenicity and metastasis of cultured CRPC cells. The present study investigated the possible synergistic effect of dmrFABP5 combined with either enzalutamide or docetaxel on suppressing the tumorigenic properties of PC cells, including cell viability, migration, invasion and colony proliferation in soft agar. A highly significant synergistic inhibitory effect on these properties was observed when dmrFABP5 was used in combination with enzalutamide on androgen-responsive PC 22RV1 cells. Moreover, a highly significant synergistic inhibitory effect was also observed when dmrFABP5 was combined with docetaxel, and added to 22RV1 cells and to the highly malignant, androgen-receptor (AR)-negative Du145 cells. DmrFABP5 alone failed to produce any suppressive effect when added to the FABP5-negative cell line LNCaP, although enzalutamide could significantly suppress LNCaP cells when used as a single agent. These synergistic inhibitory effects of dmrFABP5 were produced by interrupting the FABP5-related signal transduction pathway in PC cells. Thus, dmrFABP5 appears to be not only a potential single therapeutic agent, but it may also be used in combination with existing drugs to suppress both AR-positive and AR-negative PC.

It Takes Two to Tango: The Interplay between Prostate Cancer and Its Microenvironment from an Epigenetic Perspective

Prostate cancer is the second most common cancer in men worldwide and is associated with high morbidity and mortality. Consequently, there is an urgent unmet need for novel treatment avenues. In addition to somatic genetic alterations, deviations in the epigenetic landscape of cancer cells and their tumor microenvironment (TME) are critical drivers of prostate cancer initiation and progression. Unlike genomic mutations, epigenetic modifications are potentially reversible. Therefore, the inhibition of aberrant epigenetic modifications represents an attractive and exciting novel treatment strategy for castration-resistant prostate cancer patients. Moreover, drugs targeting the epigenome also exhibit synergistic interactions with conventional therapeutics by directly enhancing their anti-tumorigenic properties by "priming" the tumor and tumor microenvironment to increase drug sensitivity. This review summarizes the major epigenetic alterations in prostate cancer and its TME, and their involvement in prostate tumorigenesis, and discusses the impact of epigenome-targeted therapies.

[Mechanisms of cancer drug resistance]

Despite decades of research into the molecular mechanisms of cancer and the development of new treatments, drug resistance persists as a major problem. This is in part due to the heterogeneity of cancer, including the diversity of tumor cell lineage and cell plasticity, the spectrum of somatic mutations, the complexity of microenvironments, and immunosuppressive characteristic, then necessitating the use of many different therapeutic approaches. We summarize here the biological causes of resistance, thus offering new perspectives for tackle drug resistance.

Emerging frontiers in nanomedicine targeted therapy for prostate cancer

Prostate cancer is a prevalent cancer in men, often treated with chemotherapy. However, it tumor cells are clinically grows slowly and is heterogeneous, leading to treatment resistance and recurrence. Nanomedicines, through targeted delivery using nanocarriers, can enhance drug accumulation at the tumor site, sustain drug release, and counteract drug resistance. In addition, combination therapy using nanomedicines can target multiple cancer pathways, improving effectiveness and addressing tumor heterogeneity. The application of nanomedicine in prostate cancer treatment would be an important strategy in controlling tumor dynamic process as well as improve survival. Thus, this review highlights therapeutic nanoparticles as a solution for prostate cancer chemotherapy, exploring targeting strategies and approaches to combat drug resistance.

International Union of Basic and Clinical Pharmacology CXIII: Nuclear Receptor Superfamily-Update 2023

The NR superfamily comprises 48 transcription factors in humans that control a plethora of gene network programs involved in a wide range of physiologic processes. This review will summarize and discuss recent progress in NR biology and drug development derived from integrating various approaches, including biophysical techniques, structural studies, and translational investigation. We also highlight how defective NR signaling results in various diseases and disorders and how NRs can be targeted for therapeutic intervention via modulation via binding to synthetic lipophilic ligands. Furthermore, we also review recent studies that improved our understanding of NR structure and signaling. SIGNIFICANCE STATEMENT: Nuclear receptors (NRs) are ligand-regulated transcription factors that are critical regulators of myriad physiological processes. NRs serve as receptors for an array of drugs, and in this review, we provide an update on recent research into the roles of these drug targets.

Functional implications and therapeutic targeting of androgen response elements in prostate cancer

The androgen receptor (AR) plays an essential role in the growth and progression of prostate cancer (CaP). Ligand-activated AR inside the nucleus binds to the androgen response element (ARE) of the target genes in dimeric form and recruits transcriptional machinery to facilitate gene transcription. Pharmacological compounds that inhibit the AR action either bind to the ligand binding domain (LBD) or interfere with the interactions of AR with other co-regulatory proteins, slowing the progression of the disease. However, the emergence of resistance to conventional treatment makes clinical management of CaP difficult. Resistance has been associated with activation of androgen/AR axis that restores AR transcriptional activity. Activated AR signaling in resistance cases can be mediated by several mechanisms including AR amplification, gain-of-function AR mutations, androgen receptor variant (ARVs), intracrine androgen production, and overexpression of AR coactivators. Importantly, in castration resistant prostate cancer, ARVs lacking the LBD become constitutively active and promote hormone-independent development, underlining the need to concentrate on the other domain or the AR-DNA interface for the identification of novel actionable targets. In this review, we highlight the plasticity of AR-DNA binding and explain how fine-tuning AR's cooperative interactions with DNA translate into developing an alternative strategy to antagonize AR activity.

Biomarkers for Prostate Cancer: From Diagnosis to Treatment

Prostate cancer (PCa) is a widespread malignancy with global significance, which substantially affects cancer-related mortality. Its spectrum varies widely, from slow-progressing cases to aggressive or even lethal forms. Effective patient stratification into risk groups is crucial to therapeutic decisions and clinical trials. This review examines a wide range of diagnostic and prognostic biomarkers, several of which are integrated into clinical guidelines, such as the PHI, the 4K score, PCA3, Decipher, and Prolaris. It also explores the emergence of novel biomarkers supported by robust preclinical evidence, including urinary miRNAs and isoprostanes. Genetic alterations frequently identified in PCa, including BRCA1/BRCA2, ETS gene fusions, and AR changes, are also discussed, offering insights into risk assessment and precision treatment strategies. By evaluating the latest developments and applications of PCa biomarkers, this review contributes to an enhanced understanding of their role in disease management.

Regulation of Epithelial-Mesenchymal Transitions by Alternative Splicing: Potential New Area for Cancer Therapeutics

The epithelial-mesenchymal transition (EMT) is a complicated biological process in which cells with epithelial phenotype are transformed into mesenchymal cells with loss of cell polarity and cell-cell adhesion and gain of the ability to migrate. EMT and the reverse mesenchymal-epithelial transitions (METs) are present during cancer progression and metastasis. Using the dynamic switch between EMT and MET, tumour cells can migrate to neighbouring organs or metastasize in the distance and develop resistance to traditional chemotherapy and targeted drug treatments. Growing evidence shows that reversing or inhibiting EMT may be an advantageous approach for suppressing the migration of tumour cells or distant metastasis. Among different levels of modulation of EMT, alternative splicing (AS) plays an important role. An in-depth understanding of the role of AS and EMT in cancer is not only helpful to better understand the occurrence and regulation of EMT in cancer progression, but also may provide new therapeutic strategies. This review will present and discuss various splice variants and splicing factors that have been shown to play a crucial role in EMT.

Castration-Resistant Prostate Cancer: From Uncovered Resistance Mechanisms to Current Treatments

Prostate cancer (PC) is the second most common cancer in men worldwide. Despite recent advances in diagnosis and treatment, castration-resistant prostate cancer (CRPC) remains a significant medical challenge. Prostate cancer cells can develop mechanisms to resist androgen deprivation therapy, such as AR overexpression, AR mutations, alterations in AR coregulators, increased steroidogenic signaling pathways, outlaw pathways, and bypass pathways. Various treatment options for CRPC exist, including androgen deprivation therapy, chemotherapy, immunotherapy, localized or systemic therapeutic radiation, and PARP inhibitors. However, more research is needed to combat CRPC effectively. Further investigation into the underlying mechanisms of the disease and the development of new therapeutic strategies will be crucial in improving patient outcomes. The present work summarizes the current knowledge regarding the underlying mechanisms that promote CRPC, including both AR-dependent and independent pathways. Additionally, we provide an overview of the currently approved therapeutic options for CRPC, with special emphasis on chemotherapy, radiation therapy, immunotherapy, PARP inhibitors, and potential combination strategies.

Pinostilbene inhibits full-length and splice variant of androgen receptor in prostate cancer

Prostate cancer is the most prevalent cancer in men worldwide and is promoted by the sex hormone androgen. Expression of androgen from the testis can be significantly reduced through castration. However, as most prostate cancer patients acquire castration resistance, additional therapeutic solutions are necessary. Although anti-androgens, such as enzalutamide, have been used to treat castration-resistant prostate cancer (CRPC), enzalutamide-resistant CRPC (Enz-resistant CRPC) has emerged. Therefore, development of novel treatments for Enz-resistant CRPC is urgent. In this study, we found a novel anti-androgen called pinostilbene through screening with a GAL4-transactivation assay. We confirmed that pinostilbene directly binds to androgen receptor (AR) and inhibits its activation and translocalization. Pinostilbene treatment also reduced the protein level and downstream gene expression of AR. Furthermore, pinostilbene reduced the protein level of AR variant 7 in the Enz-resistant prostate cancer cell line 22Rv1 and inhibited cell viability and proliferation. Our results suggest that pinostilbene has the potential to treat Enz-resistant CRPC.

Deoxynortryptoquivaline: A unique antiprostate cancer agent

The androgen receptor (AR) is a critical target in all the clinical stages of prostate cancer. To identify a new AR inhibitor, we constructed a new screening system using the androgen-dependent growth of prostate cancer cell lines as a screening indicator. We screened 50,000 culture broths of microorganisms using this screening system and found that the fermentation broth produced by a fungus inhibited androgen-dependent growth of human prostate cancer LNCaP cells without cytotoxicity. Purification of this culture medium was performed, and this resulted in deoxynortryptoquivaline (DNT) being identified as a novel inhibitor of AR function. DNT showed potent inhibition of androgen-dependent growth of human prostate cancer LNCaP cells. The AR competitor assay was performed, and DNT did not act as an AR antagonist. However, DNT inhibited AR-dependent transcriptional activity and AR nuclear translocation, it suggested that the suppression of AR function leads to inhibition activity against androgen-dependent growth.

Targeting the Androgen Signaling Axis in Prostate Cancer

Activation of the androgen receptor (AR) and AR-driven transcriptional programs is central to the pathophysiology of prostate cancer. Despite successful translational efforts in targeting AR, therapeutic resistance often occurs as a result of molecular alterations in the androgen signaling axis. The efficacy of next-generation AR-directed therapies for castration-resistant prostate cancer has provided crucial clinical validation for the continued dependence on AR signaling and introduced a range of new treatment options for men with both castration-resistant and castration-sensitive disease. Despite this, however, metastatic prostate cancer largely remains an incurable disease, highlighting the need to better understand the diverse mechanisms by which tumors thwart AR-directed therapies, which may inform new therapeutic avenues. In this review, we revisit concepts in AR signaling and current understandings of AR signaling-dependent resistance mechanisms as well as the next frontier of AR targeting in prostate cancer.

Beyond Prostate Cancer: An Androgen Receptor Splice Variant Expression in Multiple Malignancies, Non-Cancer Pathologies, and Development

Multiple studies have demonstrated the importance of androgen receptor (AR) splice variants (SVs) in the progression of prostate cancer to the castration-resistant phenotype and their utility as a diagnostic. However, studies on AR expression in non-prostatic malignancies uncovered that AR-SVs are expressed in glioblastoma, breast, salivary, bladder, kidney, and liver cancers, where they have diverse roles in tumorigenesis. AR-SVs also have roles in non-cancer pathologies. In granulosa cells from women with polycystic ovarian syndrome, unique AR-SVs lead to an increase in androgen production. In patients with nonobstructive azoospermia, testicular Sertoli cells exhibit differential expression of AR-SVs, which is associated with impaired spermatogenesis. Moreover, AR-SVs have been identified in normal cells, including blood mononuclear cells, neuronal lipid rafts, and the placenta. The detection and characterization of AR-SVs in mammalian and non-mammalian species argue that AR-SV expression is evolutionarily conserved and that AR-SV-dependent signaling is a fundamental regulatory feature in multiple cellular contexts. These discoveries argue that alternative splicing of the AR transcript is a commonly used mechanism that leads to an expansion in the repertoire of signaling molecules needed in certain tissues. Various malignancies appropriate this mechanism of alternative AR splicing to acquire a proliferative and survival advantage.

Novel Inhibitors of androgen receptor's DNA binding domain identified using an ultra-large virtual screening

Androgen receptor (AR) inhibition remains the primary strategy to combat the progression of prostate cancer (PC). However, all clinically used AR inhibitors target the ligand-binding domain (LBD), which is highly susceptible to truncations through splicing or mutations that confer drug resistance. Thus, there exists an urgent need for AR inhibitors with novel modes of action. We thus launched a virtual screening of an ultra-large chemical library to find novel inhibitors of the AR DNA-binding domain (DBD) at two sites: protein-DNA interface (P-box) and dimerization site (D-box). The compounds selected through vigorous computational filtering were then experimentally validated. We identified several novel chemotypes that effectively suppress transcriptional activity of AR and its splice variant V7. The identified compounds represent previously unexplored chemical scaffolds with a mechanism of action that evades the conventional drug resistance manifested through LBD mutations. Additionally, we describe the binding features required to inhibit AR DBD at both P-box and D-box target sites.

Lineage plasticity and treatment resistance in prostate cancer: the intersection of genetics, epigenetics, and evolution

Androgen deprivation therapy is a cornerstone of treatment for advanced prostate cancer, and the development of castrate-resistant prostate cancer (CRPC) is the primary cause of prostate cancer-related mortality. While CRPC typically develops through a gain in androgen receptor (AR) signaling, a subset of CRPC will lose reliance on the AR. This process involves genetic, epigenetic, and hormonal changes that promote cellular plasticity, leading to AR-indifferent disease, with neuroendocrine prostate cancer (NEPC) being the quintessential example. NEPC is enriched following treatment with second-generation anti-androgens and exhibits resistance to endocrine therapy. Loss of RB1, TP53, and PTEN expression and MYCN and AURKA amplification appear to be key drivers for NEPC differentiation. Epigenetic modifications also play an important role in the transition to a neuroendocrine phenotype. DNA methylation of specific gene promoters can regulate lineage commitment and differentiation. Histone methylation can suppress AR expression and promote neuroendocrine-specific gene expression. Emerging data suggest that EZH2 is a key regulator of this epigenetic rewiring. Several mechanisms drive AR-dependent castration resistance, notably AR splice variant expression, expression of the adrenal-permissive 3βHSD1 allele, and glucocorticoid receptor expression. Aberrant epigenetic regulation also promotes radioresistance by altering the expression of DNA repair- and cell cycle-related genes. Novel therapies are currently being developed to target these diverse genetic, epigenetic, and hormonal mechanisms promoting lineage plasticity-driven NEPC.

Discovery of a Small-Molecule Inhibitor Targeting the Androgen Receptor N-Terminal Domain for Castration-Resistant Prostate Cancer

The current mainstay therapeutic strategy for advanced prostate cancer is to suppress androgen receptor (AR) signaling. However, castration-resistant prostate cancer (CRPC) invariably arises with restored AR signaling activity. To date, the AR ligand-binding domain (LBD) is the only targeted region for all clinically available AR signaling antagonists, such as enzalutamide (ENZ). Major resistance mechanisms have been uncovered to sustain the AR signaling in CRPC despite these treatments, including AR amplification, AR LBD mutants, and the emergence of AR splice variants (AR-Vs) such as AR-V7. AR-V7 is a constitutively active truncated form of AR that lacks the LBD; thus, it can not be inhibited by AR LBD-targeting drugs. Therefore, an approach to inhibit AR through the regions outside of LBD is urgently needed. In this study, we have discovered a novel small molecule SC428, which directly binds to the AR N-terminal domain (NTD) and exhibits pan-AR inhibitory effect. SC428 potently decreased the transactivation of AR-V7, ARv567es, as well as full-length AR (AR-FL) and its LBD mutants. SC428 substantially suppressed androgen-stimulated AR-FL nuclear translocation, chromatin binding, and AR-regulated gene transcription. Moreover, SC428 also significantly attenuated AR-V7-mediated AR signaling that does not rely on androgen, hampered AR-V7 nuclear localization, and disrupted AR-V7 homodimerization. SC428 inhibited in vitro proliferation and in vivo tumor growth of cells that expressed a high level of AR-V7 and were unresponsive to ENZ treatment. Together, these results indicated the potential therapeutic benefits of AR-NTD targeting for overcoming drug resistance in CRPC.

Cancer Stem Cells and Prostate Cancer: A Narrative Review

Cancer stem cells (CSCs) are a small and elusive subpopulation of self-renewing cancer cells with the remarkable ability to initiate, propagate, and spread malignant disease. In the past years, several authors have focused on the possible role of CSCs in PCa development and progression. PCa CSCs typically originate from a luminal prostate cell. Three main pathways are involved in the CSC development, including the Wnt, Sonic Hedgehog, and Notch signaling pathways. Studies have observed an important role for epithelial mesenchymal transition in this process as well as for some specific miRNA. These studies led to the development of studies targeting these specific pathways to improve the management of PCa development and progression. CSCs in prostate cancer represent an actual and promising field of research.

Murine toxicology and pharmacokinetics of lead next generation galeterone analog, VNPP433-3β

VNPP433-3β (compound 2, (3β-(1H-imidazole-1-yl)-17-(1H-benzimidazole-1-yl)-androsta-5,16-diene), a multitarget anticancer agent has emerged as our lead next generation galeterone analogs (NGGA). Compound 2 is currently in development as potential new therapeutic for prostate and pancreatic cancers. The preliminary toxicity study reveals that the compound 2 was better tolerated by the normal male CD-1 mice than the male Nude mice. The maximum tolerated dose (MTD) in the Nude mice was estimated to be between 25 < 50 mg/kg. After oral dosing of compound 2 to male and female rats, the plasma concentration versus time curves were very consistent between animals and the AUClast increased with dose. Many plasmas concentration versus time curves profiles were nearly flat over 24 hr., suggesting extended absorption from the GI tract. Consequently, reliable values for half-life and AUCinf were not determined. Calculated oral bioavailability (using oral AUClast and excluding the outlier IV animal) ranged from 32 to 47 %. This should be considered a minimum value since the contribution to true AUC beyond 24 hr. is clearly not zero. Clearly, these toxicology and pharmacokinetics parameters pave the way for understanding the anticancer pharmacological actions and provide a meaningful basis for further preclinical development and eventual clinical development.